Chronic pain affects nearly 70 million people a year in the United States and costs billions of dollars in medical treatment and lost productivity. To date, all investigations concerning the blood-brain barrier (BBB) and the delivery of analgesics have been performed in naive non-pained animals. It is becoming increasingly clear that the blood-brain barrier is not a static barrier but can be modulated by a number of factors from the immune, neuronal and hormonal systems. During pain all three of these systems are activated. The hypothesis of this study is that pain activates the immune, neuronal and hormonal systems leading to an alteration in the molecular and functional properties in the blood-brain barrier. This alteration will lead to a change in the transport of substances across the blood-brain barrier and may have a role in the etiology of chronic pain. In preliminary studies, we have seen an increase in the permeability of the rat blood-brain barrier during three models of peripheral pain (Formalin, A-carrageenan, Complete Freunds Adjuvant) to [S14C] Sucrose which will only cross the blood-brain barrier if the tight junctions have been compromised. In parallel Western blot studies we observed a reduction in occiudin (an integral BBB tight junction protein) and an increase in ZO-1 and actin (an accessory and cytoskeletal protein respectively). This indicates that the pain has altered BBB tight junctions. ELISA and ribonuclease protection assays, show that levels of TNF-a in peripheral blood and TNF-a, IFN-gamma, and interleukins 5 and 6 are altered in the CNS in a time dependent manner during A-carrageenan induced pain. All of these substances have previously been shown to alter tight junction proteins. Therefore, this proposal is designed to further investigate the changes induced by pain and the mechanisms that promote these changes by utilizing the tools of physiology, molecular biology and pharmacology in an integrative manner. It is our long-term aim to identify pharmacological agents that can treat these alterations in the blood-brain barrier.